Hello, and thank you!
Your report is confusing, since there is not STR_ADVENT in the entire mod... It was removed in 1.8, so almost a year ago, and you shouldn't be seeing these missions and ships.
The best way to fix this is to ignore any Advent vessels until the end of the month and hope that the mission list is updated correctly. If this doesn't help (usually when there's an Advent base or embassy), let me know.
So I've proceeded to the subsequent month (with the prior month being full of Advent craft) and simulated a month in advance. I am pleased to tell you there have been no Advent vessel sightings. However, I have discovered an "ALIEN COLONY-1" in Japan which, judging by a swarm of Advent vessels in East Asia last month, was put there while they were still active and I was unable to respond without crashing the game.
It is also the case that whenever I click directly on the colony, or when I send a vessel there, the game crashes citing a segmentation fault.
I've included attachments of a savegame and a game log for each mode of crash.
At this point I am happy to continue my game without any action, and simply ignore this colony provided its not going to cause me too much grief, but I thought I would leave a report anyway.
Thankyou!
EDIT: So on my actual playthrough, ten days into the new month I've discovered the colony has spawned in an Advent craft. So that is happening.